1. Field of the Invention
This invention is in the field of methods and apparatus for ventilating an occupied space in conjunction with heating and cooling the air in the occupied space by controlling the amount of outside air introduced to maintain the oxygen content of the air in the occupied space within a predetermined range, particularly when the outside air needs to be heated or cooled, to minimize the energy used in heating or cooling the air flowing through said space.
2. Description of the Prior Art
Systems for ventilating occupied spaces, spaces occupied primarily by humans such as commercial office buildings, theaters, auditoriums and the like and for heating or cooling the air being circulated through such occupied spaces are commonplace. Such prior art systems control primarily the temperature of the air being introduced into the occupied space by heating or cooling the air and controlling the amount of return air mixed with outside air to maintain the temperature and humidity of the air in the space within predetermined limits, or ranges of values.
In addition to the temperature and relative humidity, another characteristic of air of importance to the occupants of such a space is the amount of oxygen present in the air being circulated through the space. In prior art systems the amount of oxygen in the air of an occupied space has not been treated as a controllable variable such as temperature but rather as a constant.
Past methods of assuring that the amount of oxygen present in the air in an occupied space was at least adequate have required that from 5 to 7 cubic feet per minute of outside air per person for the maximum number of persons permitted in the space be introduced into the space by the ventilating system, or have required that 50 percent of the air flowing into the space be outside air. The amount of outside air introduced into such spaces is usually determined by local building codes. Essentially all such building codes require at any time a given space is occupied, that outside air be introduced into the space on the basis of the maximum occupancy of the space rather than on the actual occupancy at any given time, or to state it another way, on the basis of the rate oxygen is being used or consumed.
The introduction of fixed amounts of outside air whenever the space being ventilated is occupied, particularly when the temperature or humidity, or both, of the outside air is such that the predetermined mixture of outside air and return air must be heated or cooled, greatly increases the amount of energy required to maintain the temperature and humidity of the air in the space within desired limits compared with the amount of energy consumed if the amount of outside air introduced were based on the amount needed to maintain the oxygen content of the air in the space within an acceptable range of values.